(Download) UPSC IAS Mains Exam Paper - 2017 : Electrical Engineering
Time Allowed : Three Hours
Maximum Marks : 250
QUESTION PAPER SPECIFIC INSTRUCTIONS
(Please read each of the following instructions carefully
before attempting questions)
There are EIGHT questions divided in two Sections and printed both in
HINDI and in ENGLISH.
Candidate has to attempt FIVE questions in all.
Question Nos. 1 and 5 are compulsory and out of the remaining,
THREE are to be attempted choosing at least ONE question from each
The number of marks carried by a question/part is indicated against it.
Answers must be written in the medium authorized in the Admission Certificate
which must be stated clearly on the cover of this Question-cum-Answer (QCA)
Booklet in the space provided. No marks will be given for answers written in a
medium other than the authorized one.
Assume suitable data, if considered necessary and indicate the same clearly.
Unless otherwise mentioned, symbols and notations carry their usual standard
Attempts of questions shall be counted in sequential order. Unless struck
off, attempt of a question shall be counted even if attempted partly. Any page
or portion of the page left blank in the Question-cum-Answer Booklet must be
clearly struck off.
1. (a) For the circuit shown in Fig. 1(a), find the current through 5 2
resistor by using Thevenin's theorem and verify the same by using superposition
(b) A continuous time signal X(t) is shown in Fig. 1(b). Sketch and label each
of the following signals :
(i) x(t) u(2-t)
(ii) x(t) d(t-7/2)
(c) Show that for a distortionless transmission line, the attenuation
constant a. does not depend on frequency, whereas the
phase constant b depends linearly on it.
(d) For thie circuit given in Fig- 1(d)
(i) draw the input and output waveforms;
(ii) find the average value of the output voltage waveform.
Assume that the diode in the circuit is ideal.
(e) A 15-hp, 220-V, 3-phase, 50 Hz, 6-pole, Y-connected induction Instrar has
the following parameters per phase :
r1 = 0.128 W, r2 = 0.0935
W, (x1 + x2) = 0.496
W, re = 183 W,
xf = 8 W
The rotational losses are equal to the stator core losses (hysteresis and
eddy-current). For a slip of 3%, find the line current and power factor.
2. (a) For the Boolean function
F (W, X, Y, Z) = [0, 2, 5, 6, 7, 8, 10, 13)
(i) find all the prime implicants;
(ii) give minimal representation;
(iii) find minimal two-level realization using NAND gates only.
(b) (i) What is meant by an infinite transmission line? Also, explain the
term 'electrical length' of a transmission line. In what units is it measured?
(ii) Determine the electrical length of a 20 m long transmission line operating
at 1 MHz, if u = 0.7c on the line. Take c = 3 x 108 m/s.
(c) Discuss the properties of a probability density function. What additional
features a normal distribution has?
3. (a) The following test data were taken on a 30-kVA, 2400/240V, 50-Hz,
single-phase transformer :
Open-circuit test : V = 2400V, I = 0.3 A, P = 230 W
Short-circuit test : V = 70V, I = 18.8 A, P = 1050 W
Determine the primary voltage, real and reactive power input, and efficiency,
when a current of 12.5 A at 240 V is drawn from the low-voltage side by a load
of 0.8 p.f. lagging.
(b) A three-phase uncontrolled diode rectifier supplies a constant load
current of 10 A and its supply voltage is 400 , V 1ine-to-line. Determine the
following performance measures :
(i) Average output voltage
(ii) Supply r.m.s. current
(iii) Supply fundamental r.m.s. Current
(iv) Supply 3rd, 5th, 7th and 9th harmonic r.m.s. current
(v) Supply current displacement factor
(vi) Supply power factor
(vii) AC power (supply power)
(vii) Dc power (load power)
(c) Consider the R-L-C circuit showri in Fig. 3(c), wherein
4. (a) Explain and differentiate between the single sideband (SSB)
modulation and double sideband suppressed carrier (DSB-SC) modulation Show the
DSB-SC modulated waveform for any chosen base band signal waveform and spectrum
of the base band and the DSB-SC modulated wave,
(b) Find the Laplace transform of the function f(t) = u (sin 2t).
(c) Find the average voltage at the point Vo, in the circuit given in
Fig. 4(c) :
SECTION - B
5. (a) Prove that AB + BC + AC = AB + BC.
(b) An industrial consumer is operating a 1 kW induction motor at a lagging
power factor of 0.8 and at a source voltage of 200V, r.m.s. In order to reduce
expenditure on power consumption, he wishes to raise the power factor to 0.95
lagging by connecting a circuit element in parallel with the load. Indicate the
type of the circuit element (inductive or capacitive) and find the value if the
operating frequency is 50 Hz.
(c) (i) Explain the operation of Boost converter with voltage and current
waveforms across the Boost inductor. Assume continuous conduction.
(ii) Derive its output voltage equation in terms of duty cycle and input
(d) An amplitude modulated signal, viewed on an oscilloscope, has a crest
voltage of 44 V peak-to-peak. The bottom (or trough) point of the wave measures
6V peak-to-peak. Find the modulation factor, percentage modulation and
peak-to-peak un-modulated carrier voltage.
(e) Obtain z-parameters of a two-port network in terms of its ABCD Parameters.
6. (a) Find the value of average current flow through the load resistor
for the circuit given in Fig. 6(a).
(b) Find the value of r.m.s. current drawn from the source.
(b) Determine the transfer function and there from the impulse response of
the causal linear time invariant system described by the difference equation
y[n] - 1/4 y[n-1] - 3/8 y[n-2] = -x [n] + 2x [n-1]
(c) (i) Draw the circuit diagram of Wien bridge oscillator using OP-AMP.
(ii) Find the value of R to get a sustained oscillation of 1115 Hz. Assume that
the value of the capacitor is 0.1 uF.
7. (a) The electric field and magnetic field in free space are given by
Express these fields in phasor form and determine the constants Ho,
and bsuch that these fields satisfy Maxwell's
equations. The permeability and permittivity of the free space are 4px
10-7 H/m and 8.854 x 10-12 F/m. respectively.
(b) Find the state transition diagram and rcalization using J-K flip-flops to
count Mod 7 in the following sequence :
000, 001, 011, 100, 101, 111
(c) A 230-V, 10-hp DC series motor draw a line current of 36 A, when
delivering rated power at its rated speed of 1200 r.p.m. The armature circuit
resistance is 0.2W and the series field winding
resistance is 0.1W. The magnetization curve may
be considered linear.
(i) Find the speed of this motor when it draws a line current of 20 A.
(ii) What is the developed torque at the new condition?
8. (a) A 400-V, 3-phase balanced source is connected to an unbalanced
D-connected load of impredance Zab =
10+ 45oW, Zca = 10 - 0oW and Zca
= 10 - 45oW.Determine the
line currents (in phasor form), total active (real) and reactive power.
(b) (i) Draw the circuit diagram of a bandpass filter using OP-AMP. Its
parameters are fL = 300 Hz, fH = 2 kHz arad
passband gain is 4.
(ii) Calculate thie value of Q, Assume that the capacitor value is 0.01
(c) Differentiate between stationary and non-stationary random processes.
Give the properties of the first- and second-order distribution function of
stationary random processes.